Weather Whys: What makes a storm severe?

Weather Whys

Thunderstorms form often in the late spring, summer and early fall. Some are stronger than others, and some are considered severe. You might wonder what makes a storm “severe.” What is the criteria used to issue a warning for one storm but not another?

The criteria for a severe thunderstorm are based on hail size, wind strength and the threat of a tornado. When one or more of these conditions are met or expected to be met, a warning is issued to give people nearby time to prepare and get to safety.

Hail can be incredibly damaging, but the amount of hail is not necessarily important when warning a storm. A storm may dump a lot of very small hail in an area, but a warning might not be issued. If you’re wondering why, take a moment to measure the hail that fell. If it is under an inch, it is not considered severe, even if it buried your yard. Hail that is 1 inch or more is considered severe. A report of hail this large or radar indication that the hail is this large or might become 1 inch or more will trigger a warning.

Wind is another big factor, and can also cause damage on its own. Winds of 58 mph or more will trigger a severe thunderstorm warning. Strong winds can cause damage to trees, fences, power lines and more, and can be very dangerous. Just because a warning is issued only for wind, does not mean it should be ignored.

Of course, when a tornado is reported or suspected to be possible, a warning will also be immediately issued. It is important to take these warnings seriously because they are very dangerous.

Some dangerous weather does not warrant a severe thunderstorm warning. All thunderstorms have lightning. No matter how loud it is or how much lightning is present, a warning will not be issued for the storm. Flooding is also a threat with thunderstorms. Warnings for flooding are handled separately and do not make a storm “severe.”

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